(*Transport).RoundTrip

Description

RoundTrip executes a single HTTP transaction using the Transport's
Token as authorization headers.

This method will attempt to renew the Token if it has expired and may return
an error related to that Token renewal before attempting the client request.
If the Token cannot be renewed a non-nil os.Error value will be returned.
If the Token is invalid callers should expect HTTP-level errors,
as indicated by the Response's StatusCode.